This is a note to let you know that I've just added the patch titled
objtool: Support Clang non-section symbols in ORC generation
to the 4.19-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
objtool-support-clang-non-section-symbols-in-orc-generation.patch
and it can be found in the queue-4.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From e81e0724432542af8d8c702c31e9d82f57b1ff31 Mon Sep 17 00:00:00 2001
From: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Date: Wed, 1 Apr 2020 13:23:27 -0500
Subject: objtool: Support Clang non-section symbols in ORC generation
From: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
commit e81e0724432542af8d8c702c31e9d82f57b1ff31 upstream.
When compiling the kernel with AS=clang, objtool produces a lot of
warnings:
warning: objtool: missing symbol for section .text
warning: objtool: missing symbol for section .init.text
warning: objtool: missing symbol for section .ref.text
It then fails to generate the ORC table.
The problem is that objtool assumes text section symbols always exist.
But the Clang assembler is aggressive about removing them.
When generating relocations for the ORC table, objtool always tries to
reference instructions by their section symbol offset. If the section
symbol doesn't exist, it bails.
Do a fallback: when a section symbol isn't available, reference a
function symbol instead.
Reported-by: Dmitry Golovin <dima@xxxxxxxxxx>
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Tested-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
Reviewed-by: Miroslav Benes <mbenes@xxxxxxx>
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://github.com/ClangBuiltLinux/linux/issues/669
Link: https://lkml.kernel.org/r/9a9cae7fcf628843aabe5a086b1a3c5bf50f42e8.1585761021.git.jpoimboe@xxxxxxxxxx
Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
tools/objtool/orc_gen.c | 33 ++++++++++++++++++++++++++-------
1 file changed, 26 insertions(+), 7 deletions(-)
--- a/tools/objtool/orc_gen.c
+++ b/tools/objtool/orc_gen.c
@@ -100,11 +100,6 @@ static int create_orc_entry(struct secti
struct orc_entry *orc;
struct rela *rela;
- if (!insn_sec->sym) {
- WARN("missing symbol for section %s", insn_sec->name);
- return -1;
- }
-
/* populate ORC data */
orc = (struct orc_entry *)u_sec->data->d_buf + idx;
memcpy(orc, o, sizeof(*orc));
@@ -117,8 +112,32 @@ static int create_orc_entry(struct secti
}
memset(rela, 0, sizeof(*rela));
- rela->sym = insn_sec->sym;
- rela->addend = insn_off;
+ if (insn_sec->sym) {
+ rela->sym = insn_sec->sym;
+ rela->addend = insn_off;
+ } else {
+ /*
+ * The Clang assembler doesn't produce section symbols, so we
+ * have to reference the function symbol instead:
+ */
+ rela->sym = find_symbol_containing(insn_sec, insn_off);
+ if (!rela->sym) {
+ /*
+ * Hack alert. This happens when we need to reference
+ * the NOP pad insn immediately after the function.
+ */
+ rela->sym = find_symbol_containing(insn_sec,
+ insn_off - 1);
+ }
+ if (!rela->sym) {
+ WARN("missing symbol for insn at offset 0x%lx\n",
+ insn_off);
+ return -1;
+ }
+
+ rela->addend = insn_off - rela->sym->offset;
+ }
+
rela->type = R_X86_64_PC32;
rela->offset = idx * sizeof(int);
Patches currently in stable-queue which might be from jpoimboe@xxxxxxxxxx are
queue-4.19/objtool-support-clang-non-section-symbols-in-orc-generation.patch
